class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode* cur1=l1;
        ListNode* cur2=l2;
        ListNode* newhead=new ListNode(0);
        ListNode* tail=newhead;
        //进位
        int t=0;
        while(cur1||cur2||t)
        {
           if(cur1)
           {
                t+=cur1->val;
                cur1=cur1->next;
           } 

           if(cur2)
           {
                t+=cur2->val;
                cur2=cur2->next;
           }
           tail->next=new ListNode(t%10);
           tail=tail->next;
           t/=10;
        }
        tail=newhead->next;
        delete newhead;
        return tail;
    }
};